The Epidemiology of Alopecia Areata

A Population-based Cohort Study in UK Primary Care

M. Harries; A.E. Macbeth; S. Holmes; W.S. Chiu; W.R. Gallardo; M. Nijher; S. de Lusignan; C. Tziotzios; A.G. Messenger

Disclosures

The British Journal of Dermatology. 2022;186(2):257-265. 

In This Article

Results

Alopecia Areata Incidence

Of the total study population (n = 4 163 162), 6765 people developed new-onset AA over the study period [Figure S1 (patient flow diagram); see Supporting Information]. The overall AA IR was 0·26 per 1000 person-years. AA incidence peaked at age 25–29 years in both males [IR 0·51, 95% confidence interval (CI) 0·46–0·56] and females (IR 0·43, 95% CI 0·39–0·48). The median age at diagnosis was 31 [interquartile range (IQR) 21–41] for males and 34 (IQR 22–48) for females. The incidence peak was much broader in females than males with female incidence being higher in childhood (age groups 5–14 years) and in those people aged 45+ years [Figure 1 and Table S1 (see Supporting Information)]. AA annual IRs were stable over the 10-year study period (Figure S2; see Supporting Information). Incidence of 'nonspecific' and 'other specified' alopecia were constant over the study period (Figure S3; see Supporting Information).

Figure 1.

The incidence rates of AA by age at diagnosis and sex. Data are unadjusted incidence rates per 1000 person-years for 2009–2018 inclusive in a total population of 4 163 162 people. Grey shading represents 95% confidence intervals. AA, alopecia areata.

When adjusted for age and other sociodemographic characteristics, incident AA was more common in females (IRR 1·19, 95% CI 1·13–1·24), with the largest sex difference in people aged 50 years and above (Table 1). AA was substantially more common in nonwhite ethnicity groups with the highest incidence in Asians [IRR Asian vs. white ethnicity 3·32 (95% CI 3·11–3·55)]. Trends were consistent across the lifespan (Table 1). Incidence was highest in those with the highest levels of deprivation, and there was higher incidence among urban than rural dwellers (Table 1).

The unadjusted incidence of AA was highest in the London region [overall (adults and children combined) IRR 0·42 (95% CI 0·40–0·45)] (Table S2; see Supporting Information). In adjusted analysis, there was a lower incidence of AA in the East Midlands, North West, South East and South West compared with London [Figure 2, Table S3 (see Supporting Information)]. No significant differences by region were observed in children, although numbers were smaller (Table S3).

Figure 2.

The geographic distribution of alopecia areata by region in England. Data are adjusted incidence rate ratios, relative to the London region, with adjustment for sex, ethnicity, Index of Multiple Deprivation quintile, geographic region and geographic area (urban/rural location). Estimates are for 2009–2018 inclusive in 4 078 143 people with a postcode mapped to an English region.

Alopecia Areata Point Prevalence

There were 2 634 083 actively registered people on 31 December 2018 who were included in the estimation of AA point prevalence. Overall point prevalence (95% CI) of AA in adults was 0·58% (0·57–0·59), with a higher adult point prevalence in females [0·62% (0·60–0·63)] than males [0·55% (0·53–0·56)]. Point prevalence of nonspecific alopecia was 0·91% (0·90–0·93), and was markedly higher in females [1·57% (1·54–1·59)] than males [0·27% (0·26–0·28)]; point prevalence of other-specified alopecia was much lower [overall 0·082% (0·078–0·086); females 0·063% (0·058–0·068); males 0·100% (0·094–0·117)].

Primary Care Visits

Primary care visit rates (95% CI) for people diagnosed with AA in the year following their diagnosis were 4·32 (4·27–4·38) visits per year compared with 2·58 (2·56–2·60) in matched controls (Tables S4 and S5; see Supporting Information). Primary care visit rates for people diagnosed with AA increased over the 10-year study period and were consistently higher than visit rates for controls (Figure S4; see Supporting Information). Females made more visits than males and there was evidence of a socioeconomic gradient with more frequent visits made by those with the highest levels of deprivation. People with AA of mixed ethnicity had a lower rate of visits compared with the other ethnic groups. People with AA living in rural geographic areas made more visits than those living in urban areas (Table S4).

Specialist Dermatology Reviews

There were 1624 (24%) AA cases referred for specialist dermatology review in the year after diagnosis (Table S4). The proportion of AA cases referred increased over the study period from 19·4% (16·1–22·7) in 2009 to 27·9% (24·7–31·0) in 2017 (Figure 3). Although referrals levels were similar by ethnicity and rural/urban geography, they were higher for females (compared with males) and people living in less deprived areas (compared with those from more deprived areas) (Table S4).

Figure 3.

Proportion of people with alopecia areata (AA) referred for specialist dermatology review within 1 year of diagnosis, by calendar year. Data are for 6187 people with AA (2018 data are not reported due to insufficient follow-up time after AA diagnosis). Grey shading represents 95% confidence intervals.

Prescribing Patterns

Of the total patients, 46% did not receive any prescription medication. Potent TCS were the most commonly prescribed medications in the year after AA diagnosis, and prescribing increased over the study period (23·6% in 2009, 33·1% in 2017, Figure S5; see Supporting Information). The proportion of people prescribed mild or very potent TCS remained similar across the study period ranging between 12% and 17% (Figure S5). Of note, approximately 5% of patients were prescribed systemic steroids. Minoxidil (70 prescriptions) and dithranol (16 prescriptions) were rarely prescribed. The results were similar when people with a diagnosis of atopic dermatitis or psoriasis prior to either AA diagnosis or first medication prescription were excluded (Figure S6; see Supporting Information).

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